1. Field of the Invention
The present invention relates to a water pump, and particularly relates to a water pump which circulates cooling water of a water-cooled internal combustion engine within the internal combustion engine.
2. Description of the Related Art
Conventionally, with a water-cooled internal combustion engine 1 shown in FIG. 5 for example, a water pump 2 is disposed to perform cooling of the internal combustion engine 1.
The water pump 2 is disposed integrally to a crank case 3 of the internal combustion engine 1, and driven by a crank shaft 4 which is accommodated in the crank case 3. With this structure, cooling water which is cooled by a radiator, not shown in figures, is led to a water jacket 6 in a cylinder block 5 of the internal combustion engine 1 for example, and the cooling is performed.
As shown in FIG. 6, the water pump 2 comprises a pump body 7, a pump shaft 9 which is rotatably supported by the pump body 7 in a piercing state and to which an impeller 8 is attached at one end portion, and a mechanical seal 10 which is elastically disposed between the side of the pump shaft 9 where the impeller 8 is attached and the pump body 7.
The mechanical seal 10 is constructed by a seal member 11 and a spring 12 which elastically urges the seal member 11 towards the impeller 8.
Here, when the mechanical seal 10 is disposed, contact pressure between the mechanical seal 10 and the impeller 8 has to be ensured. Further, the dislodging of the pump shaft 9 from the pump body 7 by the urging force of the mechanical seal 10 has to be prevented. For these purposes, a dislodging prevention pin 13 is disposed to the pump shaft 9 opposite to the side where the impeller 8 is attached, being in contact with the pump body 7, so as to receive force in the thrust direction generated by the mechanical seal 10.
Further, the pump shaft 9 has a two-point mounting structure that a midway portion is rotatably supported by the pump body 7, and an end portion is rotatably supported by the crank case 3 to which the pump body 7 is attached. For example, FIG. 1 of Japanese Utility-model Kokoku H6-31197 discloses this structure.
Furthermore, FIG. 7 shows another structure example of the water pump 2 of the related art. With this water pump 2, a flange 14 is integrally formed at the midway portion of the pump shaft 9 so as to receive the force in the thrust direction generated by the mechanical seal 10 and prevent dislodging of the pump shaft 9. For example, FIG. 1 of Japanese Patent Laid-open 2000-87744 discloses this structure.
Here, since the pump shaft 9 of the abovementioned former water pump 2 is supported by two points which are apart from each other, it has following problems to be solved.
Specifically, because one of the supporting points of the pump shaft 9 is disposed at the pump body 7, and the other supporting point is disposed at the crank case 3 to which the pump body 7 is attached, the axes of the two supporting points have to be aligned accurately. As a result, there arises a problem that high accuracy machining is required and the manufacturing cost is increased.
Further, in addition to the abovementioned machining accuracy of the supporting points, since the assembling accuracy of the pump body 7 with the crank case 3 affects the abovementioned alignment accuracy, there arises a problem that the assembling process becomes complicated.
Next, with the abovementioned latter water pump 2, because the pump shaft 9 is supported at one point, the problems of the former water pump 2 are solved. However, since the flange 14 to prevent dislodging has to be formed integrally with the pump shaft 9, following problems have to be solved.
Specifically, because the flange 14 is formed integrally with the pump shaft 9, a simple machining method, such as centerless grinding, cannot be adopted when grinding the outer face of the pump shaft 9. As a result, there arises a problem that the manufacturing cost is increased.
Further, as mentioned above, because the flange 14 is formed integrally with the pump shaft 9, at the time of assembling, the impeller 8 has to be attached to the pump shaft 9 after the pump shaft 9 is inserted to the pump body 7. Therefore, the impeller 8 cannot be assembled with the pump shaft 9 in advance.
As a result, the assembling process is restricted.
The present invention was devised in the light of the abovementioned problems. The object is to provide a water pump which machining accuracy and assembling accuracy can be easily improved.